Inner surface multi-micropore double-layer pipe and air film resistance reduction test installation force transmission structure

Abstract

The invention discloses an inner surface multi-micropore double-layer pipe and an air film resistance reduction test installation force transfer structure, the double-layer pipe comprises a sliding bearing with a flange, a transparent acrylic outer layer pipe, a multi-micropore stainless steel inner layer pipe and a sliding shaft pipe with a flange, the transparent acrylic outer layer pipe sleeves the multi-micropore stainless steel inner layer pipe, and the transparent acrylic outer layer pipe sleeves the multi-micropore stainless steel inner layer pipe; an annular-pipe-shaped air cavity is formed between the sliding bearing and the sliding shaft pipe, annular embedding and inserting parts are formed at the ends, with flanges, of the sliding bearing and the sliding shaft pipe respectively, the annular embedding and inserting parts of the sliding bearing and the sliding shaft pipe are embedded into the two ends of the annular-pipe-shaped air cavity respectively and sealed in a gluing mode, an air inlet is formed in the sliding bearing, and air enters the annular-pipe-shaped air cavity from the air inlet through an air pipe connector. Uniform air pressure is formed in the annular-pipe-shaped air cavity, so that air in the cavity can evenly penetrate through the multi-micropore stainless steel inner-layer pipe, a uniform air film is formed on the inner wall face of the multi-micropore stainless steel inner-layer pipe, and the air film can be regulated and controlled by regulating and controlling the air inlet pressure and the air flow.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid resistance measurement, in particular to a double-layer tube with multi-micro pores on the inner surface, an air film drag reduction test installation force transmission structure and a preparation process thereof. Background Art

[0002] In the field of fluid mechanics testing, water tunnel testing and wind tunnel testing are two important ways to obtain experimental data. They can not only obtain the forces exerted on the test model in the fluid medium, but also observe the interaction between the test model and the fluid. The water tunnel has a stable and controllable water flow. During the test, the test model remains stationary or rotates while the water flows. Wind tunnel testing is an experimental method for obtaining the air resistance of models such as aircraft, automobiles, and high towers. However, the construction project of the wind tunnel is huge, costly, the experimental process is complex, and the preparation cycle is long. These problems seriously restrict the popularization and promotion of wind resistance testing. CN103018002A discloses a test device and a test method for measuring the wind resistance of an automobile model. It uses a fan to generate simulated wind, and this feature makes the wind speed that can be obtained by this device relatively low, with large noise and vibration. A physical simulation test device for air film drag reduction and its test method disclosed by South China University of Technology with the application number 201910182663.2. Since the front part of its model is a conical tip, the gas or liquid flow directly impacts on the conical tip. The positive impact force received by the conical tip of the model is much greater than the axial fluid friction force received by the outer surface of the straight wall of the model. The axial force measured by the dynamometer is the sum of the axial fluid impact force received by the conical tip axially and the axial fluid friction force received by the outer surface of the straight wall of the model. The air film drag reduction effect is to evaluate the difference between the axial fluid friction forces received by the outer surface of the straight wall of the model with and without an air film on the outer surface of the straight wall of the model, that is, the axial fluid friction force received by the outer surface of the straight wall of the model with an air film minus the axial fluid friction force received by the outer surface of the straight wall of the model without an air film, and calculate the numerical difference between the two. If the measured parameter includes the positive impact force of the gas or liquid flow directly impacting on the conical tip instead of directly measuring the axial fluid friction force received by the outer surface of the straight wall of the model, it will increase the measurement error. At the same time, due to the high-speed fluid impacting on the conical tip of the model, the positive impact force is very large and the flow rate is very fast, the model will generate high-frequency tremors and vibrations, affecting the stability and accuracy of the measurement. Summary of the Invention

[0003] The purpose of the present invention is to overcome the disadvantages of long construction period, large investment, and cumbersome operation in the prior art, and provide a double-layer tube with multi-micro pores on the inner surface, an air film drag reduction test installation force transmission structure and a preparation process thereof, which have a simple and compact structure, easy operation, stable and reliable testing, and low cost.

[0004] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0005] A double-layer tube with multi-micro-pores on the inner surface, comprising a sliding bearing with a flange, a transparent acrylic outer tube, a multi-micro-pore stainless steel inner tube, and a sliding shaft tube with a flange. The transparent acrylic outer tube is sleeved outside the multi-micro-pore stainless steel inner tube, and an annular air cavity is formed between them. The ends of the sliding bearing and the sliding shaft tube with flanges respectively form annular insertion parts that can be inserted into the annular air cavity. The shape and size of the annular insertion parts match those of the annular air cavity. The annular insertion parts of the sliding bearing and the sliding shaft tube are respectively inserted into both ends of the annular air cavity and are glued and sealed. An air inlet hole for threadedly connecting an air pipe joint is provided on the sliding bearing. The air inlet hole communicates the air pipe joint with the annular air cavity. Gas enters the annular air cavity from the air inlet hole through the air pipe joint, forming a uniform air pressure in the annular air cavity. Thus, the gas in the cavity can uniformly pass through the multi-micro-pore stainless steel inner tube, forming a uniform air film on the inner wall surface of the multi-micro-pore stainless steel inner tube, and the air film can be regulated by controlling the inlet air pressure and air flow rate.

[0006] Preferably, the sliding bearing and the sliding shaft tube are made of aluminum alloy.

[0007] An air film drag reduction test installation force transmission structure for the air film drag reduction test of the above double-layer tube with multi-micro-pores on the inner surface, comprising an outflow pipe ring support seat, an outflow pipe, a force transmission rod, a vertical plate strip, an inflow pipe ring support seat, and a stepped inflow pipe. The outflow pipe ring support seat supports the middle diameter section of the outflow pipe. The inner hole surface of the outflow pipe is in precise sliding fit with the outer surface of the sliding shaft tube. The outlet of the outflow pipe is connected to a bent pipe joint so that the fluid is discharged from the side. The inflow pipe ring support seat supports the maximum diameter section of the stepped inflow pipe. The outer diameter surface of the outlet of the stepped inflow pipe is in precise sliding fit with the inner hole surface of the sliding bearing. There are two force transmission rods. The two force transmission rods are symmetrically distributed above and below the outflow pipe with respect to the axial center line of the outflow pipe and are parallel to each other. One end of the two force transmission rods is fixed to the flange of the sliding shaft tube, and the other end is connected by a vertical plate strip to assemble the two force transmission rods together. The central part of the vertical plate strip is connected to the force measuring head of a precision dynamometer. When the fluid flows through the multi-micro-pore stainless steel inner tube, it will form a frictional force on the inner surface of the multi-micro-pore stainless steel inner tube, causing the multi-micro-pore stainless steel inner tube to have a tendency to move along the tube axis direction. The force is transmitted to the force transmission rod through the flange of the sliding shaft tube, and then transmitted to the force measuring head by the vertical plate strip, so as to measure the axial frictional force on the inner wall surface of the multi-micro-pore stainless steel inner tube under the condition of having an air film. By regulating relevant parameters, the law of air film drag reduction can be studied.

[0008] Preferably, the force transmission rod and the vertical plate strip are made of aluminum alloy.

[0009] A gas film drag reduction test installation force transmission structure is used for the gas film drag reduction test of the above-mentioned double-layer tube with multi-micro-porous inner surface, and includes an outflow pipe cylinder support seat, an outflow pipe, an inflow pipe cylinder support seat, a stepped inflow pipe, and a square tube frame. The double-layer tube with multi-micro-porous inner surface passes through the square tube frame, making the axial center line of the square tube frame parallel and coincident with the axial center line of the double-layer tube with multi-micro-porous inner surface. A spacing is reserved between the outer surface of the double-layer tube with multi-micro-porous inner surface and the inner surface of the square tube frame, and they do not contact each other, so that the double-layer tube with multi-micro-porous inner surface can move freely along the axis. The bottom surface of the square tube frame is fixed on the workbench surface. The precision dynamometer is fixed on the upper surface of the square tube frame along the axis of the double-layer tube with multi-micro-porous inner surface, and the measuring head of the precision dynamometer is kept in contact with the flange of the sliding bearing. The outflow pipe cylinder support seat supports the middle diameter section of the outflow pipe. The inner hole surface of the outflow pipe is in precise sliding fit with the outer surface of the sliding shaft tube. The outlet of the outflow pipe is connected to an elbow joint, so that the fluid is discharged from the side. The inflow pipe cylinder support seat supports the maximum diameter section of the stepped inflow pipe. The outer diameter surface of the outlet of the stepped inflow pipe is in precise sliding fit with the inner hole surface of the sliding bearing. The inner surface of the multi-micro-porous stainless steel inner layer tube is subjected to the frictional force of the fluid movement in the tube, causing the double-layer tube with multi-micro-porous inner surface to have a tendency to slide along the axis. The frictional force received is transmitted through the flange to the measuring head of the precision dynamometer, so as to precisely measure the axial frictional force of the double-layer tube with multi-micro-porous inner surface under the condition of gas film under the action of the fluid. By adjusting the relevant parameters, the law of gas film drag reduction can be studied.

[0010] A preparation process for the above-mentioned double-layer tube with multi-micro-porous inner surface includes the following steps:

[0011] 1) Material preparation: Making a metal porous strip from a metal wire material;

[0012] 2) Mesh preparation: Folding the made metal porous strip into a multi-layer metal porous wire mesh;

[0013] 3) Pressing: Pressing the folded multi-layer metal porous wire mesh to make the wire mesh flat;

[0014] 4) Rolling: Rolling the pressed multi-layer metal porous wire mesh to achieve mechanical bonding between the multi-layers of wire mesh;

[0015] 5) Sintering: Sintering the rolled multi-layer metal porous wire mesh to achieve metallurgical bonding between the multi-layers of wire mesh and form a metal porous plate;

[0016] 6) Component manufacturing: Making the sintered metal porous plate into a double-layer tube with multi-micro-porous inner surface.

[0017] Preferably, in step 2), the metal porous strip is folded in a Z-shaped manner.

[0018] Preferably, in step 3), place the multi-layer metal porous wire mesh horizontally directly below the straightening machine press head. Lower the press head and hold the pressure for 30 seconds at the automatically reached maximum pressure.

[0019] Preferably, in step 4), place the multi-layer metal porous wire mesh horizontally in front of the roller feed inlet, keep it parallel to the roller gap. Adjust the roller gap to the minimum, and feed the multi-layer metal porous wire mesh into the rolling area for trial rolling. If it is impossible to feed the multi-layer metal porous wire mesh due to the small roller gap, gradually increase the roller gap until the rolling is successful.

[0020] Preferably, in step 5), horizontally clamp the rolled multi-layer metal porous wire mesh between two layers of sintered bricks so that the gradually formed metal porous plate during the sintering process remains flat. Put the sintered bricks and the multi-layer metal porous wire mesh into a vacuum sintering furnace for sintering.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. It can directly and accurately measure the axial frictional force of the fluid on the inner surface of the pipe. By comparing the changes in the axial frictional force of the fluid received by the double-layer pipe in different states with and without an air film under the conditions of ventilating or not ventilating the double-layer pipe, the effect of air film drag reduction can be tested.

[0023] 2. The support seats are respectively installed on the inlet pipe and the outlet pipe. The two ends of the double-layer pipe are respectively sleeved inside the mouths of the inlet pipe and the outlet pipe. The two ends of the double-layer pipe are supported by the inlet pipe and the outlet pipe, and the double-layer pipe is in a suspended state and can freely axially slide in the pipe axis direction. The double-layer pipe has no direct fixed support, avoiding the frictional force caused by the support members, reducing the measurement error, and the measured data is accurate and reliable.

[0024] 3. The double-layer pipe avoids the frontal impact force received by the conical model, does not generate high-frequency tremors and vibrations, and the measurement results are relatively stable.

[0025] 4. The present invention has a compact structure, is easy to operate, and has stable testing. It can be widely used for fluid resistance testing of small-scale models such as aircraft, submarines, torpedoes, and underwater vehicles, and can provide important and valuable references for the optimization design and performance determination of physical objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of a double-layer pipe with multi-micro-pores on the inner surface.

[0027] Figure 2 It is a partial cross-sectional view of the upper flange part of the sliding bearing (showing the air inlet holes).

[0028] Figure 3 It is a schematic diagram of one of the air film drag reduction test installation force transmission structures.

[0029] Figure 4 It is a schematic diagram of another force transmission structure for gas film drag reduction test installation. Specific implementation mode

[0030] The present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings, but the implementation modes of the present invention are not limited thereto.

[0031] Embodiment 1

[0032] As Figure 1 shown, this embodiment discloses a double-layer tube with multi-micro-porous inner surface, including a sliding bearing 1 with a flange, a transparent acrylic outer layer tube 3, a multi-micro-porous stainless steel inner layer tube 4, and a sliding shaft tube 6 with a flange. The transparent acrylic outer layer tube 3 is sleeved outside the multi-micro-porous stainless steel inner layer tube 4, and an annular air cavity 12 is formed between them. The sliding bearing 1 and the sliding shaft tube 6 are aluminum alloy parts, and annular insertion parts that can be inserted into the annular air cavity 12 are respectively formed at their ends with flanges. The shape and size of the annular insertion parts match those of the annular air cavity 12. The annular insertion parts of the sliding bearing 1 and the sliding shaft tube 6 are respectively inserted into both ends of the annular air cavity 12 and are glued and sealed. An air inlet hole 2 for threadedly connecting an air pipe joint is provided on the sliding bearing 1. As Figure 2 shown, the air pipe joint can be fixed to the air inlet hole 2 by threads. The air inlet hole 2 connects the air pipe joint with the annular air cavity 12. Gas enters the annular air cavity 12 from the air inlet hole 2 through the air pipe joint, and a uniform air pressure is formed in the annular air cavity 12. Thus, the gas in the cavity can uniformly pass through the multi-micro-porous stainless steel inner layer tube 4, and a uniform gas film is formed on the inner wall surface of the multi-micro-porous stainless steel inner layer tube 4. The gas film can be regulated by controlling the intake air pressure and air flow rate.

[0033] The following is the preparation process of the above-mentioned double-layer tube with multi-micro-porous inner surface in this embodiment, including the following steps:

[0034] 1) Material preparation: Making a metal porous strip from a metal wire material;

[0035] 2) Mesh preparation: Folding the made metal porous strip into a multi-layer metal porous wire mesh in a Z-shaped folding manner;

[0036] 3) Pressing: Pressing the folded multi-layer metal porous wire mesh to make the wire mesh flat; among them, placing the multi-layer metal porous wire mesh horizontally directly below the pressing head of the straightening machine, lowering the pressing head, and maintaining the pressure for 30 seconds at the maximum pressure automatically reached;

[0037] 4) Rolling: Roll the pressed multi-layer metal porous wire mesh to achieve mechanical bonding between the multi-layer wire meshes. Specifically, place the multi-layer metal porous wire mesh horizontally in front of the feed inlet of the rolling mill, keep it parallel to the roll gap, adjust the roll gap to the minimum, send the multi-layer metal porous wire mesh into the rolling area for trial rolling. If the multi-layer metal porous wire mesh cannot be sent in due to the small roll gap, gradually increase the roll gap until successful rolling is achieved.

[0038] 5) Sintering: Sinter the rolled multi-layer metal porous wire mesh to achieve metallurgical bonding between the multi-layer wire meshes and form a metal porous plate. Specifically, horizontally clamp the rolled multi-layer metal porous wire mesh between two sintering bricks to keep the metal porous plate gradually formed during the sintering process flat, and then place the sintering bricks and the multi-layer metal porous wire mesh into a vacuum sintering furnace for sintering.

[0039] 6) Component manufacturing: Manufacture the sintered metal porous plate into a double-layer tube with many micro-pores on the inner surface.

[0040] Example 2

[0041] As Figure 3 shown, this example discloses a gas film drag reduction test installation force transmission structure for the gas film drag reduction test of the double-layer tube with many micro-pores on the inner surface described in Example 1, which includes an outflow pipe ring support seat 7, an outflow pipe 8, a force transmission rod 9, a vertical slat 11, an inflow pipe ring support seat 13, and a stepped inflow pipe 14. The outflow pipe ring support seat 7 supports the middle diameter section of the outflow pipe 8. The inner hole surface of the outflow pipe 8 is in precise sliding fit with the outer surface of the sliding shaft tube 6, and there is no gap between the mating surfaces but they can slide freely. The outlet of the outflow pipe 8 is connected to an elbow joint so that the fluid is discharged from the side. The inflow pipe ring support seat 13 supports the maximum diameter section of the stepped inflow pipe 14. The outer diameter surface of the outlet of the stepped inflow pipe 14 is in precise sliding fit with the inner hole surface of the sliding bearing 1, and there is no gap between the mating surfaces but they can slide freely. There are two force transmission rods 9, which are made of aluminum alloy. The two force transmission rods 9 are symmetrically distributed above and below the outflow pipe 8 with respect to the axial center line of the outflow pipe 8 and are parallel to each other. One end of each of the two force transmission rods 9 is fixed to the flange 5 of the sliding shaft tube 6, and the other ends are connected by the vertical slat 11 to assemble the two force transmission rods 9 together. The vertical slat 11 is made of aluminum alloy, and the center part thereof is connected to the force measuring head 10 of a precision dynamometer. When the fluid flows through the multi-micro-pore stainless steel inner layer tube 4, a frictional force will be formed on the inner surface of the multi-micro-pore stainless steel inner layer tube 4, causing the multi-micro-pore stainless steel inner layer tube 4 to have a tendency to move along the tube axis direction. The force is transmitted to the force transmission rod 9 through the flange 5 of the sliding shaft tube 6, and then transmitted to the force measuring head 10 by the vertical slat 11, so as to measure the axial frictional force on the inner wall surface of the multi-micro-pore stainless steel inner layer tube 4 under the condition of having a gas film. By adjusting relevant parameters, the law of gas film drag reduction can be studied.

[0042] Among them, the support seat is respectively installed on the inlet pipe and the outlet pipe, and the two ends of the double-layer pipe are respectively sleeved in the mouths of the inlet pipe and the outlet pipe. The two ends of the double-layer pipe are supported by the inlet pipe and the outlet pipe. The double-layer pipe is in a suspended state and can slide freely in the axial direction of the pipe. The double-layer pipe has no direct fixed support, which avoids the friction caused by the support, reduces the measurement error, and the measured data is accurate and reliable. The layout of the inner surface diameters of the variable-diameter inlet pipe 14, the double-layer pipe, and the outlet pipe 8 are successively larger, which facilitates the smooth forward flow of the fluid in the channel and can prevent the fluid from leaking at the sliding fit of the pipe hole.

[0043] Example 3

[0044] like Figure 4 As shown, this embodiment discloses an air film drag reduction test installation force transmission structure, which is used for the air film drag reduction test of the inner surface multi-microporous double-layer tube described in Example 1, including an outlet tube annular tube support seat 7, an outlet tube 8, an inlet tube annular tube support seat 13, a variable diameter inlet tube 14 and a square tube frame 16, the inner surface multi-microporous double-layer tube passes through the square tube frame 16, so that the axial center line of the square tube frame 16 is parallel to and coincides with the axial center line of the inner surface multi-microporous double-layer tube, a spacing is reserved between the outer surface of the inner surface multi-microporous double-layer tube and the inner surface of the square tube frame 16, and the two are not in contact, so that the inner surface multi-microporous double-layer tube can move freely in the axial direction, the bottom surface of the square tube frame 16 is fixed on the workbench, the precision dynamometer 15 is fixed to the upper surface of the square tube frame 16 along the axial direction of the inner surface multi-microporous double-layer tube, and the force measuring head 10 of the precision dynamometer 15 is aligned with the sliding bearing 1's flange keeps in contact, the outlet pipe annular tube support seat 7 is supported on the middle pipe diameter section of the outlet pipe 8, the inner hole surface of the outlet pipe 8 is precisely slidably matched with the outer surface of the sliding shaft tube 6, the outlet of the outlet pipe 8 is connected to a bend pipe joint, so that the fluid is discharged from the side, the inlet pipe annular tube support seat 13 is supported on the maximum pipe diameter section of the variable diameter inlet pipe 14, the outlet outer diameter surface of the variable diameter inlet pipe 14 is precisely slidably matched with the inner hole surface of the sliding bearing 1, the inner surface of the multi-microporous stainless steel inner layer pipe 4 is subjected to the friction force of the fluid movement in the pipe, resulting in the multi-microporous double-layer pipe on the inner surface having a tendency to slide axially, and the friction force is transmitted to the force measuring head 10 of the precision dynamometer 15 through the flange, so as to accurately measure and obtain the axial friction force of the multi-microporous double-layer pipe on the inner surface under the condition of air film. By adjusting the relevant parameters, the law of air film drag reduction can be studied.

[0045] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A double-layer tube with multiple micropores on the inner surface, characterized in that: The invention comprises a sliding bearing (1) with a flange, a transparent acrylic outer tube (3), a multi-microporous stainless steel inner tube (4) and a sliding shaft tube (6) with a flange, wherein the transparent acrylic outer tube (3) is sleeved outside the multi-microporous stainless steel inner tube (4), and an annular air cavity (12) is formed between them, and an annular inserting portion capable of being embedded in the annular air cavity (12) is formed at one end of the sliding bearing (1) and the sliding shaft tube (6) with a flange, respectively, and the shape and size of the annular inserting portion match the annular air cavity (12), and the annular inserting portion of the sliding bearing (1) and the sliding shaft tube (6) is preferably an annular inserting portion. The insert parts are respectively embedded in the two ends of the annular tubular air cavity (12) and glued and sealed. The sliding bearing (1) is provided with an air inlet hole (2) that can be threadedly connected to the air pipe joint. The air inlet hole (2) connects the air pipe joint and the annular tubular air cavity (12). The gas enters the annular tubular air cavity (12) from the air inlet hole (2) through the air pipe joint, forming a uniform air pressure in the annular tubular air cavity (12), so that the gas in the cavity can evenly pass through the multi-microporous stainless steel inner layer tube (4), forming a uniform air film on the inner wall surface of the multi-microporous stainless steel inner layer tube (4), and the air film can be regulated by regulating the air inlet pressure and the air flow rate.

2. A double-layer tube with multiple micropores on the inner surface according to claim 1, characterized in that: The sliding bearing (1) and the sliding shaft tube (6) are aluminum alloy parts.

3. An air film drag reduction test installation force transmission structure, characterized in that: The device is used for the air film drag reduction test of the double-layer tube with multiple micropores on the inner surface as claimed in claim 1 or 2, comprising an outlet tube annular tube support seat (7), an outlet tube (8), a force transmission rod (9), a vertical slat (11), an inlet tube annular tube support seat (13) and a variable diameter inlet tube (14), wherein the outlet tube annular tube support seat (7) is supported on the middle diameter section of the outlet tube (8), the inner hole surface of the outlet tube (8) is precisely slidably matched with the outer surface of the sliding shaft tube (6), the outlet of the outlet tube (8) is connected to a bend pipe joint so that the fluid is discharged from the side, the inlet tube annular tube support seat (13) is supported on the maximum diameter section of the variable diameter inlet tube (14), the outer diameter surface of the outlet of the variable diameter inlet tube (14) is precisely slidably matched with the inner hole surface of the sliding bearing (1), and there are two force transmission rods (9), and the two force transmission rods (9) are symmetrically distributed about the axial center line of the outlet tube (8) to discharge the fluid. The two force transmission rods (9) are arranged above and below the tube (8) and are parallel to each other. One end of the two force transmission rods (9) is fixed on the flange (5) of the sliding shaft tube (6), and the other end is connected through a vertical slat (11). The two force transmission rods (9) are assembled together. The center of the vertical slat (11) is connected to the force measuring head (10) of the precision dynamometer. When the fluid flows into the multi-microporous stainless steel inner tube (4), friction force is generated on the inner surface of the multi-microporous stainless steel inner tube (4), so that the multi-microporous stainless steel inner tube (4) has a tendency to move along the tube axis. The force is transmitted to the force transmission rod (9) through the flange (5) of the sliding shaft tube (6), and then the force is transmitted to the force measuring head (10) through the vertical slat (11), so that the axial friction force of the inner wall of the multi-microporous stainless steel inner tube (4) under the condition of air film is measured. By adjusting the relevant parameters, the law of air film drag reduction can be studied.

4. The air film drag reduction test installation force transmission structure according to claim 3, characterized in that: The force transmission rod (9) and the vertical slat (11) are made of aluminum alloy.

5. An air film drag reduction test installation force transmission structure, characterized in that: The air film drag reduction test for the inner surface multi-microporous double-layer tube according to claim 1 or 2 comprises an outlet tube annular tube support seat (7), an outlet tube (8), an inlet tube annular tube support seat (13), a variable diameter inlet tube (14) and a square tube frame (16), wherein the inner surface multi-microporous double-layer tube passes through the square tube frame (16), so that the axial center line of the square tube frame (16) is parallel to and coincides with the axial center line of the inner surface multi-microporous double-layer tube, and the inner surface multi-microporous double-layer tube passes through the square tube frame (16). A space is reserved between the outer surface of the double-layer tube and the inner surface of the square cylinder frame (16), and the two are not in contact, so that the inner surface multi-microporous double-layer tube can move freely in the axial direction. The bottom surface of the square cylinder frame (16) is fixed on the workbench, and the precision dynamometer (15) is fixed on the upper surface of the square cylinder frame (16) along the axial direction of the inner surface multi-microporous double-layer tube, and the dynamometer head (10) of the precision dynamometer (15) is kept in contact with the flange of the sliding bearing (1). The outlet pipe annular tube support seat (7) is supported on the middle pipe diameter section of the outlet pipe (8), the inner hole surface of the outlet pipe (8) is precisely slidably matched with the outer surface of the sliding shaft pipe (6), the outlet of the outlet pipe (8) is connected to a bend pipe joint so that the fluid is discharged from the side, the inlet pipe annular tube support seat (13) is supported on the maximum pipe diameter section of the variable diameter inlet pipe (14), the outlet outer diameter surface of the variable diameter inlet pipe (14) is precisely slidably matched with the inner hole surface of the sliding bearing (1), the inner surface of the multi-microporous stainless steel inner layer pipe (4) is subjected to the friction force of the fluid moving in the pipe, causing the inner surface multi-microporous double-layer pipe to have a tendency to slide axially, and the friction force is transmitted to the measuring head (10) of the precision dynamometer (15) through the flange, so as to accurately measure the axial friction force of the inner surface multi-microporous double-layer pipe under the condition of air film. By adjusting the relevant parameters, the law of air film drag reduction can be studied.

6. A process for preparing a double-layer tube with multiple micropores on the inner surface as claimed in claim 1 or 2, characterized in that: The following steps are involved: 1) Material preparation: making the metal wire material into a metal porous strip; 2) Netting: fold the prepared metal porous strip into a multi-layer metal porous wire mesh; 3) Pressing: Press the folded multi-layer metal porous screen to make the screen flat; 4) Rolling: Roll the pressed multi-layer metal porous wire mesh to achieve mechanical bonding between the multi-layer wire mesh; 5) Sintering: Sintering the rolled multi-layer metal porous wire mesh to achieve metallurgical bonding between the multi-layer wire mesh to form a metal porous plate; 6) Manufacturing: The sintered metal porous plate is manufactured into a double-layer tube with multiple micropores on the inner surface.

7. The process for preparing a double-layer tube with multiple micropores on the inner surface according to claim 6, characterized in that: In step 2), the metal porous strip is folded in a Z-shape.

8. The process for preparing a double-layer tube with multiple micropores on the inner surface according to claim 6, characterized in that: In step 3), the multi-layer metal porous wire mesh is horizontally placed directly below the pressure head of the straightening machine, the pressure head is lowered, and the pressure is maintained for 30 seconds at the maximum pressure automatically reached.

9. The process for preparing a double-layer tube with multiple micropores on the inner surface according to claim 6, characterized in that: In step 4), the multi-layer porous metal screen is horizontally placed in front of the roller feed port, parallel to the roller gap, the roller gap is adjusted to the minimum, and the multi-layer porous metal screen is sent into the rolling area to try rolling. If the multi-layer porous metal screen cannot be sent in due to the small roller gap, the roller gap is gradually increased until the rolling is successful.

10. The process for preparing a double-layer tube with multiple micropores on the inner surface according to claim 6, characterized in that: In step 5), the rolled multi-layer porous metal mesh is horizontally sandwiched between two layers of sintered bricks to keep the metal porous plate gradually formed during the sintering process flat, and the sintered bricks and the multi-layer porous metal mesh are placed in a vacuum sintering furnace for sintering.

Images